1. Field of the Invention
This invention generally relates to light waveguide mediums and, more particularly, to a system and method for controlling the intensity of light extracted from a waveguide surface.
2. Description of the Related Art
FIG. 1 is a plan view of representing light extracted from a liquid crystal display (LCD) backlight (prior art). Mura is a Japanese term for unevenness, inconsistency in physical matter, or human spiritual condition. This word is used in LCD to describe undesired illumination non-uniformity due to design or fabrication defects. Mura can come from both front and back panels. As shown in the figure, more light is being extracted near the input light emitting devices (LEDs) on the left side of the panel, than on the right side of the panel. The significant amount of light extracted near the light source leaves an insufficient amount of light to be extracted from the right side of the panel. Backlight panels are conventionally designed using a significant degree of trial-and-error to find the correct balance of light extraction and illumination.
FIG. 2 is a partial cross-sectional view of a liquid crystal display (LCD) backlight system (prior art). Ideally, the system is intended to extract and collimate light (from the light source) up, through the waveguide top surface, to illuminate an LC panel (not shown).
FIG. 3 is a diagram comparing the intensity of light extracted from the waveguide top and bottom surfaces (prior art). Often, as shown in FIG. 2, a reflection pattern is added to the bottom of the waveguide to minimize the amount of light exiting the waveguide through the bottom surface. Alternatively or in addition, as shown in FIG. 2, a reflector can be added under the waveguide bottom surface. However, both these solutions undesirably increase the thickness and complexity of the backlight system.
FIG. 4 is a partial cross-sectional view of a waveguide light extraction feature (prior art). Depending on where light strikes the bubble structure, it may be reflected to the waveguide bottom surface (the rays marked “1”), extracted from the waveguide top surface (the rays marked “2”), or realigned at an angle where it is likely to strike another bubble structure at a favorable angle (the rays marked “3”).
Conventionally, rays (1) reflected to the waveguide bottom surface have been an undesirable limitation associated with the use of light extraction features.
It would be advantageous if backlight panels and waveguide devices could be more efficiently designed to control the intensity of extracted light from a specified waveguide surface.